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compress/flate: move big non-pointer arrays to end of compressor

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The compressor type is fairly large: 656616 bytes on amd64.
Before this patch, it had fields of slice and interface type
near the end of the struct. As those types always contain pointers,
the ptrBytes value in the type descriptor was quite large.
That forces the garbage collector to do extra work scanning for pointers,
and wastes a bit of executable space recording the gcmask for the type.

This patch moves the arrays to the end of the type,
fixing those minor issues.

Change-Id: I849a75a19cc61137c8797a1ea5a4c97e0f69b4db
Reviewed-on: https://go-review.googlesource.com/c/go/+/707596
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
This commit is contained in:
Ian Lance Taylor 2025-09-28 21:38:53 -07:00 • committed by Gopher Robot
parent 4ca048cc32
commit 8d6d14f5d6
1 changed files with 12 additions and 10 deletions
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22
src/compress/flate/deflate.go
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@ -89,16 +89,6 @@ type compressor struct {
step func(*compressor) // process window
bestSpeed *deflateFast // Encoder for BestSpeed
// Input hash chains
// hashHead[hashValue] contains the largest inputIndex with the specified hash value
// If hashHead[hashValue] is within the current window, then
// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
// with the same hash value.
chainHead int
hashHead [hashSize]uint32
hashPrev [windowSize]uint32
hashOffset int
// input window: unprocessed data is window[index:windowEnd]
index int
window []byte
@ -117,6 +107,18 @@ type compressor struct {
maxInsertIndex int
err error
// Input hash chains
// hashHead[hashValue] contains the largest inputIndex with the specified hash value
// If hashHead[hashValue] is within the current window, then
// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
// with the same hash value.
// These are large and do not contain pointers, so put them
// near the end of the struct so the GC has to scan less.
chainHead int
hashHead [hashSize]uint32
hashPrev [windowSize]uint32
hashOffset int
// hashMatch must be able to contain hashes for the maximum match length.
hashMatch [maxMatchLength - 1]uint32
}